Nigel Farage is alleged to have had a series of secret meetings with WikiLeaks founder Julian Assange, according to evidence given to a US congressional inquiry.

The former Ukip leader is said to have passed a “thumb drive” containing data to Mr Assange during one of their sessions at the Ecuadorian Embassy in London.

The claims – made by the co-founder of the investigative firm behind the controversial “Trump dossier” into the US president’s alleged links with Russia before he entered the White House – were dismissed by Mr Farage as “conspiratorial nonsense”.

According to a transcript of his testimony released by the House Intelligence Committee, Fusion GPS boss Glenn Simpson claimed WikiLeaks was part of a “somewhat unacknowledged relationship” between the Trump team and the “Ukip people”.

Julian Assange has been living at the Ecuadorian Embassy in London since 2012 (Dominic Lipinski/PA)

Mr Simpson was giving evidence about his firm’s investigation into Mr Trump’s affairs – initially on behalf of Republicans opposed to his nomination for the presidency and then later for a law firm acting for the Democrats.

In the course of their inquiries the firm employed former MI6 officer Christopher Steele, who produced the dossier claiming that the Russians had gathered compromising material on Mr Trump – claims fiercely denied by the president.

However, during his appearance before the committee in November, Mr Simpson said his interest in the Trump campaign’s links to Ukip and WikiLeaks were separate from Mr Steele’s investigations.

He said that Mr Farage became “someone that we were very interested in” after the EU referendum vote in June 2016.

“I still think it’s very interesting,” he said.

“And so I have formed my own opinions… that there was a somewhat unacknowledged relationship between the Trump people and the Ukip people and that the path to WikiLeaks ran through that. And I still think that today.”

Julian Assange has taken refuge in the Ecuadorian embassy (Philip Toscano/PA)

Mr Simpson said while there had been media reports of one visit Mr Farage made to the Ecuadorian Embassy – where Mr Assange has been living since 2012 to avoid extradition to Sweden – he believed there had been further contacts between the two men.

“I’ve been told and have not confirmed that Nigel Farage had additional trips to the Ecuadorian Embassy than the one that’s been in the papers and that he provided data to Julian Assange,” he said.

WikiLeaks has previously been accused by Hillary Clinton of acting as a “fully owned subsidiary of Russian intelligence” after it published damaging emails, allegedly stolen by Russian operatives, during the 2016 presidential election campaign.

Mr Farage campaigned openly for Mr Trump in the election and was one of the first visitors to meet him in Trump Tower following his victory.

Mr Trump responded by suggesting that Mr Farage should be appointed UK ambassador to the US – much to the consternation of British diplomats.